1. Field of the Invention
The invention relates to an auto-focusing apparatus using contrast.
2. Description of the Related Art
In an apparatus for auto-focusing by using contrast, a focus lens is moved, at which a high frequency component (focus evaluation value) of an image signal is greatest. A direction in which the focus lens is driven to find the greatest high frequency component is determined based on whether the high frequency component is increasing or decreasing. However, noise such as hand-shake may affect the high frequency component. To adjust for the noise that may be affect the high frequency component, a threshold value for determining whether the high frequency component is increasing or decreasing may be used. The determination of the high frequency component is often performed over a predetermined period of time to increase the reliability of the determination.
Thresholds are often used in two ways. First, a large threshold value may be used for determining whether the high frequency component is increasing or decreasing. This case may be advantageous in terms of a short lens driving time, but it may be difficult to determine whether the high frequency component is increasing or decreasing because of the high threshold value. Second, a small threshold value may be used for determining whether the high frequency component is increasing or decreasing. In this case, the lens driving time may be long, but, advantageously, whether the high frequency component is increasing or decreasing may be determined with higher reliability than with a large threshold. Both, low and high thresholds have disadvantages and finding the greatest high frequency component is very important for an in-focus image that will satisfy the consumer.